Submarine foundation and offshore working platform

ABSTRACT

A submarine foundation and offshore working platform comprising a submersible integral concrete structure adapted to be situated on the sea bottom and having hollow spaces for confining ballast, oil, water, etc. Said structure comprises a plurality of vertically arranged cylindrically shaped lower hollow bodies bound together in the contacting areas, and on the overside of said bodies a plurality of platform supporting columns extending above sea level and carrying a platform structure. The columns are provided with breakwater means which comprises a disk-shaped structure slidably mounted thereon.

United States Patent Hafskjold 3,824,943 7/1974 Mo 6l/46.5 X

OTHER PUBLICATIONS [75] Inventor: Petter Sigvardt Hafskjold,

Bekkesma, Norway The 011 and Gas Journal of Sept. 14, 1970 pp. 60 61.

[73] Assignee: Ingenior F. Selmer A/S, Oslo, P i E i j ob Shapiro NorwayAttorney, Agent, or FirmLadas, Parry, Von Gehr, [22] Filed: June 13,1973 Goldsm1th & Deschamps [21] Appl. No.: 369,694 [57] ABSTRACT Asubmarine foundation and offshore working plat- [30] Forelgn ApphcatlonPnomy Data form comprising a submersible integral concrete struc- June13, 1972 Norway 2083/72 ture adapted to be Situated on the Sea bottomand 1 ing hollow spaces for confining ballast, oil, water, etc. [52] US.Cl. 6l/46.5, 61/50 Said Structure comprises a plurality of vertically[51] Int. Cl E0211 27/38 ranged ylindrically shaped lower hollow bodies[58] F1eld of Search 61/46, 46.5, 50; 114/.5 D bound together in thecontacting areas and on the overside of said bodies a plurality ofplatform support- [56] References C'ted ing columns extending above sealevel and carrying a UNITED STATES PATENTS platform structure. Thecolumns are provided with 2,662,378 12/1953 Schmitt et al 61 /4 ater meas which comprises a disk-shaped 2,731,799 1/1956 Lange et al...... 61/4structure slidably mounted thereon. 3,605,774 9/1971 Launay et al....61/46 3,708,987 1/1973 Roulet 61/46 7 Clams, 7 Drawmg Figures 4O LL1114414 my L110 ll 11 6 ll 11 l] [I LII]; J 'l T T all 1 1 1 PATEHTED FEB5 SHEET 2 OF 3 SHEET 3 or 3 ATENTED 4197 w W "o- SUBMARINE FOUNDATIONAND OFFSHORE WORKING PLATFORM The present invention relates generally toa new design for a submarine foundation, particularly developed to beused in connection with offshore oil production and oil storage, andparticularly developed for underwater storage of oil in relativelyshallow sea vicinitics. having depths up to 100 to l50 meters.

The invention relates further to a supporting column and breakwaterstructure for submarine foundations.

When in the following specification the invention is designated as asubmarine foundation," it shall be understood that the foundation, ifdesired, may include tanks for the storage of oil. The underwaterfoundation in accordance with the invention is more particularly of thetype comprising a plurality of mutually separated, submerged vesselswhich can be utilized for storage of oil and/or ballast, and whichfurther include parts which extend above the sea level and can beutilized as a working platform, housing mechanical equipment, forming apier fundament, etc.

It is today known several designs for structures of the above mentionedtype. Of somewhat older date are known structures made in steel, whilein the later years there is developed foundations and tank constructionsmade in reinforced concrete. A special problem in connection with steelstructures is that the structures possess a large positive buoyancy andmust thus be provided with particular ballast in order to be stabilized-when submerged. Wholly or partly submerged steel constructions musttherefore in many cases be furnished with particular ballast spaceswhich are filled with sand or the like, and must still be provided withspecial anchoring in order to bind the tank construction to the seabottom. The corrosion problem implies also a substantial objection tostructures of steel, especialiy with regard to the danger for oilleakages.

A substantial advantage with constructions made in reinforced concreterests in that the concrete material makes it easier to give theconstruction the desired weight, and furthermore one avoids thecorrosion problem.

Generally one can say that in building underwater foundations designedfor the storage of oil and which preferably shall include a structureabove the sea level, it is the experience that the wave stresses andloads imply the most substantial problem. Both directly and indirectlythe wave loads imply a danger for that the structure may be damagedpresenting a risk for oil leakages, a fact which in view of the relativelarge oil quantities here spoken of, can result in extensivecontaminations and pollutions, deterioration of the fish life, beachareas etc. Safety measures constitute therefore a decisive factor whendesigning submarine and underwater foundation which also shall beutilized for offshore storage of oil. From a point of view of safetythere is again several factors which count, among others one must as faras possible avoid the risk for damages in consequence of collision withships. Damages in collision with ships may happen in result of a directcollision and in result ofa damage caused by a ship anchored to thefoundation. Wave actions may otherwise result in direct damages on thestructure, particularly the structure above sea level, and may in factresult in that the entire foundation structure is moved, such as beinglifted from the sea bottom or being displaced laterally.

It is today known that the wave forces which such structures aresubjected to may be of a vast size. As an example may be mentioned thatin the North Sea one may reckon with wave heights up to 20 meters, andthat the wave forces on the structure then may act all the way down tothe sea bottom at depths of about meters.

With the aim to provide sufficiently stable submerged structures of thetype resting on the sea bottom one has hitherto generally solved theproblem by giving the foundation sufficient width and length relative tothe height and the water depth, simultaneously as the foundations aregiven sufficient weight, with or without a load of oil.

The object of the present invention has primarily been to provide a newtype of structure presenting a large ability to withstand wave actionsof various kinds, and which furthermore is specially designed to providean effective attenuation of the-surface waves, in order to therebyincrease the usability of the structure as a working platform and as aharbor location for ships.

Further aims for the invention are to provide a construction which to alarge degree fulfils the needs for safety measures, particularly inrespect of the risk for damages, and possible oil leakages. I

A further object of the invention is to provide a construction whichsimultaneously is attractive from a technical/economical point of view.The submarine foundation in accordance with the invention is of the typecomprising a submersible integral concrete structure adapted to besituated on the sea bottom and having hollow spaces'for confiningballast, oil, water, etc., said foundation including a plurality ofadjacent, vertically arranged, prismatically or cylindrically shapedlower hollow bodies of concrete integrally bound together in thecontacting areas, said bodies having closed bottom and top walls anddesigned to rest on the sea bottom in underwater position, and on theoverside of said bodies a plurality of platform supporting columnsextending above sea level and carrying a platform structure, the bottomend of each of the columns having a cross-sectional configurationgenerally corresponding to and positioned in the zone between anyselected group of said mutually adjacently located hollow bodies andproviding support for the columns.

In a preferred embodiment of the invention the supporting columns arehollow and have a wall structure which corresponds to the shape of thebelow located parts of the pertaining hollow bodies, and comprisepreferably an integrally moulded continuation of same. If the submergedhollow bodies thus are given the shape of circular cylinders, the wallsurfaces of the supporting columns will constitute parts of three orfour cylindric surfaces, depending upon how the cylindric bodies arestacked together. If the submerged hollow bodies alternatively forinstance are given the shape of equilateral octagons, the supportingcolumns will attain a square cross-section.

It is of course not necessary to provide the construction withsupporting columns in all the available zones between a group ofadjacent cylindric hollow bodies, but one will arrange the number ofsupporting columns found necessary. In the free" zones one may in lieuof supporting columns cast a floor being flush with the top walls of thehollow bodies, the top deck or the floor in these zones may be providedwith openings, such that the spaces below can be filled with sea water.Alternatively, one may however also close off these spaces in order toutilize same for instance for storage of oil.

The supporting columns are as mentioned preferably made hollow, andhereby is provided the advantageous feature that one may obtain acontinuous raising shaft from the top of the columns at the workingplatform and down to the sea bottom. These shafts may be utilized forsituating servide pipes, etc.

The submerged hollow bodies of concrete, which hereafter for sake ofsimplicity shall be designated as the main cylinders, can be utilized toincrease the stability of the construction by filling same with masssuch as sand, or for the storage of liquids, such as water and- /or oil.A special feature of an embodiment of the invention rests in that themain cylinders at the bottom are particularly devised in order to beplaced'into engagement with the sea bottom, by providing the bottomwalls of the main cylinders at a distance above the bottom wall edgessuch that same protrude freely in direction downwards. In the hollowspaces under the bottom walls of the cylinders one may maintain asub-pressure supplied by a fluid through suitable piping means leadingto a vacuum pump equipment positioned on the working platform, and aspecial feature of the invention rests in that special pipes are leddown into the sea bottom below the foundation, such that one maymaintain a state of sub-pressure also in the mass below the foundation.A such sub-pressure will in reality increase the weight of the entirefoundation, simultaneously as the foundation will be sucked firmly downto the sea bed. These features shall be described in detail later.

The main cylinders are preferably adapted with such height that the topwall is located at a good distance below the sea surface and below thelargest draught for tank ships, etc. The supporting columns provided asfrom the top of the main cylinders serve primarily three objects, namelyfirstly to carry the platform above sea level, secondly to providebreakwater means, and thirdly to serve as access means to the maincylinders and to the basement portion of the foundation.

The breakwater structure of the invention comprises generally aplurality of upright parallelly located supporting columns extendingfrom a depth below the wave action zone in the sea and to a level abovethe sea, each of said columns provided with a disk-shaped, substantiallyhorizontally extending structure supported by and encompassing slidablyat least a number of said supporting columns, the disk-shaped structuresoperable to be positioned in any desired level on the columns.

The submarine foundation in accordance with the invention includes alsoother important features which will appear from the followingspecification, wherein the invention shall be described with referenceto the accompanying schematic drawings illustrating some embodiments ofthe invention, and wherein:

FIG. 1 is showing a schematic cross-section through a foundationconstruction in accordance with the invention, said section taken alongthe plane II-II in FIG. 2, and

FIG. 2 is showing a plan view of the construction shown in FIG. 1,

FIG. 3 is showing a plan view of a preferred embodiment of theinvention, and

FIGS. 4 and 5 are detail views which in an enlarged scale are showing aplan view and a lateral view of part of the construction shown in FIG.3, respectively; FIG.

5 showing an elevational section along the plane V-V shown in FIG. 4.

FIG. 6 is likewise showing a schematic plan view of a part of a furtherembodiment of the invention.

FIG. 7 is showing a detail view in vertical-section and showing thebottom portion of the construction and illustrating how the foundationmay be bound to the sea bottom ground.

In FIGS. I and 2 the numbers 2,2, etc. designate a number of thesocalled main cylinders, which are cast to each other side by side in aright angle positional relationship such that the foundation attains forinstance a rectangular or preferably square circumference viewed in planview such as shown in FIG. 2.

The main cylinders are cast together along all adjacent contact facesalong a suitable wide range or arcs. The main cylinders are in uprightdirection in the shown embodiment divided into three compartments namelyan upper tank space 4, a ballast space 6 and a downwardly openfoundation space 8 which is formed in that the bottom wall 9 of theballast space is drawn upwards from the cylinder side walls 10 at thebottom, whereby is formed a plurality of suction cups along the bottomside of the construction.

From the top side of the main cylinders are provided supporting columns12,12 etc., and an essential feature of the invention rests in that thesupporting columns are built upon the adjacent wall sections of anadjacent group of the main cylinders such that the walls of thesupporting columns or outer parts of same constitute a geometricalcontinuation of the below located wall parts of the cylinders. In theshown embodiment of the invention the side walls of the supportingcolumns are thus constituted by four circular arcs viewed in plan viewas indicated at 15 in FIG. 2. In practice it may be suitable to modifythe cross-sectional shape of the main cylinders such that the same areshaped as octagons or modified octagons 17 such as shown in the detailview, FIG. 6, whereby the supporting columns 19 attain squarecross-sectional shape. All wall sections in the main cylinders as wellas in the supporting columns may then be given the same width, wherebyamong other advantages is obtained that one may operate with a standardmodule, simplifying the productional equi ment and the concrete formwork.

To position the supporting columns between adjacent main cylindersimplies several substantial advantages, namely firstly that the sidewalls of the main cylinders may be directly utilized as supporting partsfor the supporting columns and in fact may constitute a directcontinuation of the main cylinder structure. Furthermore is provided acontinuous space in the form of a shaft extending from the top of thesupporting columns at the platform down to the bottom of the foundation,which shaft can be utilized for positioning pipelines, etc., to thevarious tanks and spaces in the main cylinders. Furthermore these shaftsmay be utilized for positioning special pipe lines which may serve toincrease the pressure between the base of the foundation and the sublayer, that is the sea bottom, by providing a sub-pressure below themain cylinders. This feature of the invention shall be described laterin detail.

A special advantage of the construction rests in that the size of thesupporting columns, and the shape and positioning of same imply thepossibility to arrange a very effective breakwater structure,simultaneously as the construction will not in a substantial degreehinder water flow between the supporting columns.

It is not purposely to provide the foundation construction withsupporting columns between all adjacent groups of the main cylinders. Inthe embodiment shown in FIG. 2 one has thus provided supporting columnsat the shown places 12,12, etc., that is such that about one half of thespaces are provided with supporting columns. In those spaces 13,13, etc.where columns are not provided, the foundation is provided with aconcrete flooring, possibly with openings, and which suitably is castflush with the top walls of the main cylinders, such that these spacesmay be filled with sea water. The same will count for the shafts throughthe supporting columns, since same are usually open at the bottom andthus sufficiently vented at the top at the platform 20.

The embodiment shown in plan view in FIG. 3 is hexagonal, but othershapes may be visualized, for instance triangular, such that all anglesbetween intersecting center lines between the main cylinders will be 60,the supporting columns also attaining generally triangular shape.

FIGS. 4 and 5 constitute respectively a plan view and a lateral viewseen in section along the plane VV in FIG. 4 and the Figures are showingtypical features of the foundation shown in plan view in FIG. 3.

The reference numbers 30,30 are designating the walls of the maincylinders, 32 the roof of the main cylinders, while 12 designates thesupporting columns the walls of which 34,36, 38 as shown constitutegeometrical continuations of the below located parts of each of theadjacent main cylinders. A constructional advantage of this design isthat the weight of the supporting columns, the platform and theequipment of same will be transferred down to the sea bottom via thewalls of the main cylinders as simple compression forces, a fact whichamong others implies that the roof construction of the main cylindersonly can be given the strength necessary to withstand the differencebetween the internal and the external pressures (water head). Theroofing on the main cylinders may preferably be made of reinforcedconcrete provided with beams 43 on the underside.

On the supporting columns may in accordance with the invention beprovided special breakwaters in the shape of disks 40 which preferablyare supported in hoistableand lowerable slide guides 45 and furthermorenot shown locking means such that the disks may be positioned at thedesired elevational level, usually in the level on the sea surface. Thenumber 44 is designating generally the pipelines etc. positioned in theshaft 46 extending through the supporting columns, and which pipes etc.serve as a connection from the equipment 48 in question positioned onthe platform (FIG. 1) down to the various tank spaces in the hollowcylinders and to equipment located at the bottom of the foundation andpossibly below same. When a foundation structure in accordance with theinvention is transported to the pre-selected location and has beensubmerged and anchored, the shafts between the socalled main cylindersmay be filled up with sea water, likewise a desired number of the tankspaces in the cylinders are filled with sea water with the aim to reducethe buoyancy of the foundation structure. The shafts between thecylinders not provided with columns, may have open bottoms such that theshafts are automatically filled with sea water during the submersion.

FIG. 7 is a detailed sectional, enlarged view illustrating a typicalpart of the bottom section of a foundation structure as shown in FIG. 1.As shown the downwardly protruding, free-standing portions of the walls50,50 of the cylindersare moved a distance down into the sea bottom,here designated with the number 52, partly by means of the weight of thefoundation, partly in that the sea bottom below is removed in a desireddegree (it is here pre-supposed that the sea bottom is not consisting ofstone or rock). On the outside of the cylinders located along thecircumference of the foundation is preferably positioned a stabilizingdike 54, for instance by dumping down stones and gravel. Thefree-standing wall sections 50,50 on the cylinders are in directiondownwards defining downwardly open spaces 56 which as previouslymentioned constitute suction cups directed .against the mass underneath,and these spaces may by means of pipings 58 be connected to a vacuumpump plant on the platform and subjected to a state of vacuum.Preferably one has furthermore via the shafts 46 pressed down into theground 60 special suction pipes 62, which may be positioned therein bymaking bore holes or alternatively these pipes may constitute a drillpipe string.

At the bottom end these pipes are provided with openings such that theground below the sea bottom also may be subjected to a state ofsub-pressure having into effect that the entire foundation structure infact will be pressed against the sea bottom. Practically speaking onehas hereby made the entire foundation structure heavier, since the partof the sea bottom below the foundation which is maintained to a vacuumwill constitute part of the real weight of the foundation structure.These means will to a large degree increase the stability of thefoundation structure and thus contribute to the anchoring of thefoundation to the sea bottom.

A further advantage with the suction cups" 56 and the suction means 58and 62 rests in that same may be utilized to release the foundation fromthe sea bottom when same shall be elevated and brought up to a floatingcondition, for instance in order to be transported to another location.The suction cup spaces 56 and the sea bottom are then subjected to highpressure by means of compressed air or compressed water.

In regard the dimensions of the foundation these must be adapted to thesea depths in question and the desired storing capacity for oil. Inregard the question of safety and the breakwater effect it is preferredthat the distance from the sea level down to the top wall of the maincylinders at least is approximately 15-20 meters. The height of thecylinders should obviously be conformed to the local conditions. Thesame counts for the number of supporting columns relative to the numberof cylinders. Normally it will be suitable to provide supporting columnsat about each second one of the confined areas between an adjacent groupof cylinders. In order to further reduce the danger for damage of thefoundation with oil leakages in result it may further be practical toutilize those cylinders positioned along the circumference only asballast spaces, for instance by filling same with water or sand.

In regard the supporting columns these are inherently with the generaldesign given a sidewall presenting a number of faces preferably havingconcave form, a

shape which is obtained by utilizing the shape of the areas between anyselected groupof the cylinders. Confer the configuration illustrated inFIGS. 2 and 4. A such shape will result in the particular effect thatthe wave flows are diverted or directed laterally, whereby the waterflowmay hit against oppositely directed wave flows from other supportingcolumns, whereby wave forces are dissipated. In regard the diskspositioned on the columns, same may in many cases with advantage beshaped as lenses seen in cross-section and may in some instances bedesigned such that they have a tilt.

What is claimed is:

l. A submarine foundation and offshore working platform comprising asubmersible integral concrete structure adapted to be situated on thesea bottom and having hollow spaces for confining ballast or othermaterials, said foundation including a plurality of adjacent, verticallyarranged, prismatically or cylindrically shaped lower hollow bodies ofconcrete placed in contact with one another and integrally bondedtogether at their areas of contact, said bodies having closed bottom andtop walls and being designed to rest on the sea bottom inunderwaterposition, and above said hollow bodies a plurality of platformsupporting columns each extending above seal level from the region of aninterspace defined between a set of at least three hollow bodies whichare mutually adjacently located and which are bonded each to only twoother members of the set, each wall of each column constituting anupwardly extending continuation of that part of one of the hollowbodies, of the set of hollow bodies defining the interspace from whichthe column extends, which bounds the interspace.

2. Structure as recited in claim 1, in which the lower hollow bodies areidentical and the number of hollow bodies constituting each said set isfour, the areas of contact between the hollow bodiesof each set lyingsubstantially at respective corners of a square.

3. Structure as recited in claim 1, in which the lower hollow bodies areidentical regular cylindrically-shaped bodies and the number of hollowbodies constituting each said set is three, the areas of contact betweenthe hollow bodies of each set lying substantially at respective cornersof an equilateral triangle.

4. Structure as recited in claim 1, in which said hollow bodies-areidentical octagonal prismatically-shaped bodies which are cast togetheralong common wall sections.

5. Structure as recited in claim 4, in which the octagonalprismatically-shaped bodies are regular and each platform supportingcolumn is of generally square cross-sectional shape.

6. Structure as recited in claim 1, in which the interspace defined thehollow bodies of one set and the interior of the platform supportingcolumn extending from the region of that interspace together define acontinuous upright shaft extending from the top of the column to thebottom of the interspace for positioning equipment and and providingaccess for maintenance and repair.

7. A submarine foundation and offshore working platform comprising asubmersible integral concrete structure adapted to be situated on thesea bottom and having hollow spaces for confining ballast or othermaterials, said foundation including a plurality of adjacent, verticallyarranged prismatically or cylindrically shaped lower hollow bodies ofconcrete placed in contact with one another and integrally bondedtogether at their areas of contact, said bodies having closed bottom andtop walls and being designed to rest on the sea bottom in underwaterposition, and above said hollow bodies a plurality of platformsupporting columns each extending above sea level from the region of aninterspace defined between a set of four hollow bodies which aremutually adjacently located and which are bonded each to only two otherbodies of the set, each column having four walls and each columnconstituting an upwardly extending continuation of that part of one ofthe hollow bodies, of the set of hollow bodies defining the interspacefrom which the column extends, which bounds the interspace.

1. A submarine foundation and offshore working platform comprising asubmersible integral concrete structure adapted to be situated on thesea bottom and having hollow spaces for confining ballast or othermaterials, said foundation including a plurality of adjacent, verticallyarranged, prismatically or cylindrically shaped lower hollow bodies ofconcrete placed in contact with one another and integrally bondedtogether at their areas of contact, said bodies having closed bottom andtop walls and being designed to rest on the sea bottom in underwaterposition, and above said hollow bodies a plurality of platformsupporting columns each extending above seal level from the region of aninterspace defined between a set of at least three hollow bodies whichare mutually adjacently located and which are bonded each to only twoother members of the set, each wall of each column constituting anupwardly extending continuation of that part of one of the hollowbodies, of the set of hollow bodies defining the interspace from whichthe column extends, which bounds the interspace.
 2. Structure as recitedin claim 1, in which the lower hollow bodies are identical and thenumber of hollow bodies constituting each said set is four, the areas ofcontact between the hollow bodies of each set lying substantially atRespective corners of a square.
 3. Structure as recited in claim 1, inwhich the lower hollow bodies are identical regular cylindrically-shapedbodies and the number of hollow bodies constituting each said set isthree, the areas of contact between the hollow bodies of each set lyingsubstantially at respective corners of an equilateral triangle. 4.Structure as recited in claim 1, in which said hollow bodies areidentical octagonal prismatically-shaped bodies which are cast togetheralong common wall sections.
 5. Structure as recited in claim 4, in whichthe octagonal prismatically-shaped bodies are regular and each platformsupporting column is of generally square cross-sectional shape. 6.Structure as recited in claim 1, in which the interspace defined thehollow bodies of one set and the interior of the platform supportingcolumn extending from the region of that interspace together define acontinuous upright shaft extending from the top of the column to thebottom of the interspace for positioning equipment and and providingaccess for maintenance and repair.
 7. A submarine foundation andoffshore working platform comprising a submersible integral concretestructure adapted to be situated on the sea bottom and having hollowspaces for confining ballast or other materials, said foundationincluding a plurality of adjacent, vertically arranged prismatically orcylindrically shaped lower hollow bodies of concrete placed in contactwith one another and integrally bonded together at their areas ofcontact, said bodies having closed bottom and top walls and beingdesigned to rest on the sea bottom in underwater position, and abovesaid hollow bodies a plurality of platform supporting columns eachextending above sea level from the region of an interspace definedbetween a set of four hollow bodies which are mutually adjacentlylocated and which are bonded each to only two other bodies of the set,each column having four walls and each column constituting an upwardlyextending continuation of that part of one of the hollow bodies, of theset of hollow bodies defining the interspace from which the columnextends, which bounds the interspace.